1. Field of the Invention
The present invention generally relates to a mobile broadcast system. More particularly, the present invention relates to an apparatus and method for managing a preference channel based on Lightweight Application Scene Representation (LASeR) in a mobile broadcast system.
2. Description of the Related Art
Lightweight Application Scene Representation (LASeR) is a format of multimedia content for a simple multimedia service in terminals such as mobile phones suffering from resource shortages. The LASeR may be a sub-set of a Moving Picture Experts Group-4 Binary Format for Scene (MPEG-4 BIFS). The BIFS is a scene description standard for all multimedia contents and the LASeR is a scene description standard for multimedia terminals such as mobile phones in which a display size and a network bandwidth are small.
The BIFS is used for an object-based system. In the object-based system, multimedia is a set of objects. Accordingly, temporal and spatial information of each of the media needs to be indicated. For example, in the case of a weather forecast, four objects such as a weather caster, a weather chart displayed behind the weather caster, speech of the weather caster, and background music can be considered. When multiple objects are present independently, an appearing time, disappearing time and position of each object should be defined to describe one scene. This definition is the BIFS. Because related information is stored in a binary file according to the BIFS, the storage capacity is reduced.
However, the BIFS has a large amount of data of about 200 pages as described in the MPEG-4 system standard document (International Organization for Standardization/International Electro-technical Commission (ISO/IEC) 14496-1). Thus, in communication environments suffering from the shortage of available resources as in mobile terminals, there is a difficulty in using the BIFS. An alternative plan is to use the LASeR. The LASeR is the technology developed for free representations of various multimedia and interactions with users in mobile terminals with limited memory and power by performing multiplexing and synchronization processes for different elementary streams (ESs) such as a LASeR scene description, video, audio, image, font, and metadata, and minimizing complex requirements.
The LASeR ES is constructed with an access unit (AU) including a command. The command is used to change a scene characteristic at a particular time. Simultaneous commands are grouped in one AU. The AU may be one scene image, short sound, one graphic image, or short animation. The commands are Insert, Replace, Delete, Background, Save, Clean, and the like. The LASeR may be referred to as the standard needed to express a commercial film (CF) in which images vary with very complex elements. A LASeR browser displays ESs in designated order. The hierarchy is present between the ESs. The LASeR browser displays scenes in order of: (1) packet reception, (2) packet decoding (AU-by-AU recovery of one image, one video clip, and the like), (3) command execution, (4) audio/video object rendering, (5) user interaction (selection, dragging, and the like), and (6) local connection or connection with an external information source.
FIG. 1 is a block diagram illustrating a multi-stream transceiver in a conventional mobile broadcast system. A conventional preference channel composition method based on the LASeR will be described with reference to FIG. 1.
In FIG. 1, a transmitter 100 is a server of a broadcast provider and a receiver 120 is a mobile terminal for receiving a mobile broadcast service.
The conventional transmitter 100 includes a preference channel compositor 101. The preference channel compositor 101 of the transmitter 100 composes multiple channels designated by the broadcast provider in one image and transmits the image on an additional channel. Then, a mobile terminal user can retrieve the multiple channels in service from one image of the receiver 120 and can select a channel designated by the broadcast provider. The receiver includes a reception section 121, a demultiplexer 123, decoding buffers 125, a decoder 127, a composition memory 129 and a compositor 131.
In this preference channel composition method, the mobile terminal user cannot directly select his/her preference channel. That is, the mobile terminal user cannot select a channel according to his/her intention, preference and taste.
FIG. 2 illustrates a delay time due to channel switching in the conventional mobile broadcast system. An amount of delay time occurring at the channel switching time will be described with reference to FIG. 2.
In the mobile broadcast system, power consumption of a data reception section (not illustrated) for receiving data significantly affects that of a terminal. To address this problem, the mobile broadcast system such as a digital video broadcast-handheld (DVB-H) system periodically transmits data and operates the data reception section when desired data is transmitted. In other cases, the data reception section does not operate according to a time slicing scheme, such that power consumption is reduced. System parameters as shown in Table 1 are considered according to DVB-H implementation guideline.
TABLE 1System ParametersValuesChannel bandwidth8MHzData transmission rate10MbpsError correction (MPE-FEC buffer) size2MbitsData transmission rate per channel500Kbps
A delay time occurring at the channel switching time is computed by system parameters as shown in Table 1.
Assuming that the time occupied by one channel is 200 ms required to transmit 2 Mbits and a total of 20 channels are present, a transmission period becomes 4 sec. as illustrated in FIG. 2.
At this time, the time required to switch a channel in the mobile broadcast system such as the DVB-H system is a sum of a waiting time until an associated channel transmission period is reached and a time required to search for and decode an I-frame of video data from an associated channel. As illustrated in FIG. 2, when a change to channel-B 203 is made while channel-C 201 is received, a transmission time of a maximum of 4 sec corresponding to the channel transmission period is required. In this case, when the transmission time of 4 sec is added to 2 sec corresponding to the time required to start decoding after searching for the I-frame of the video, a delay time occurring at the channel switching time becomes a total of 6 sec. Thus, when a channel is switched, the mobile terminal user feels tedium due to the delay time.
Accordingly, there is a need for an improved apparatus and method for reducing a delay time in a mobile broadcast system when a channel is switched in a mobile broadcast system.